When a hearing aid is placed in and removed from the ear, feedback noise can occur. This is because of a large change in the acoustic transfer function (hereinafter “acoustic system”) between the microphone collecting sound and the receiver outputting sound.
Art for feedback noise suppression control in a hearing aid is disclosed, for example, by Patent Literature 1 and Patent Literature 2.
In the art in Patent Literature 1, in a case where the state in which the level of a particular frequency signal is prominent in the collected sound signal from the microphone continues, feedback noise is judged to have occurred, and the volume of the acoustic signal is reduced. In the art in Patent Literature 2, a touch sensor by electrodes is provided in a hearing aid, and the timing of the placing in or removing from the ear of the hearing aid is detected by the existence or non-existence of contact with the skin, at which time the volume of the acoustic signal is reduced.
According to the above-noted conventional art, feedback noise caused by placement in and removal from the ear can be reduced or prevented.